Generally, the widely-used peripheral input device of a computer system includes for example a mouse device, a keyboard device, a trackball device, or the like. Via the keyboard device, characters or symbols can be inputted into the computer system directly. As a consequence, most users and most manufacturers of input devices pay much attention to the development of keyboard devices.
The structures and the functions of a conventional keyboard device 1 will be illustrated as follows. Please refer to FIGS. 1, 2, 3 and 4. FIG. 1 is a schematic perspective view illustrating the outer appearance of a conventional keyboard device. FIG. 2 is a schematic exploded view illustrating a portion of the keyboard device as shown in FIG. 1 and taken along a viewpoint. FIG. 3 is a schematic exploded view illustrating a portion of the keyboard device as shown in FIG. 1 and taken along another viewpoint. FIG. 4 is a schematic cross-sectional view illustrating a portion of the keyboard device as shown in FIG. 1. For succinctness, only one key structure and the related components are shown in FIGS. 1, 2, 3 and 4. In practice, the keyboard device comprises one or more than one key structure.
The conventional keyboard device 1 comprises plural key structures 10, a base plate 11 and a membrane circuit board 12. The membrane circuit board 12 is arranged between the key structures 10 and the base plate 11. Each key structure 10 comprises a keycap 101, a connecting element 102 and an elastic element 103. The connecting element 102 is connected between the keycap 101 and the base plate 11. Consequently, the keycap 101 is movable upwardly or downwardly relative to the base plate 11. The elastic element 103 is arranged between the keycap 101 and the base plate 11. Moreover, the elastic element 103 comprises a contacting part 1031. For example, the connecting element 102 is a scissors-type connecting element. Moreover, the connecting element 102 comprises a first frame 1021 and a second frame 1022. The second frame 1022 is pivotally coupled to the first frame 1021. Each keycap 101 comprises a locking part 1011 and a hooking part 1012.
The base plate 11 comprises a first hook 111 and a second hook 112. The first hook 111 and the second hook 112 are protruded upwardly and penetrated through the corresponding circuit board openings 125 of the membrane circuit board 12. A first end of the first frame 1021 is connected with the hooking part 1012 of the keycap 101. A second end of the first frame 1021 is connected with the second hook 112 of the base plate 11. A first end of the second frame 1022 is connected with the locking part 1011 of the keycap 101. A second end of the second frame 1022 is connected with the first hook 111 of the base plate 11. Due to the above design, the first frame 1021 and the second frame 1022 can be swung relative to each other. That is, the first frame 1021 and the second frame 1022 are selectively switched from a stacked state to an open-scissors state or switched from the open-scissors state to the stacked state.
The membrane circuit board 12 comprises plural membrane switches 121. While the keycap 101 of any key structure 10 is depressed and moved downwardly relative to the base plate 11, the first frame 1021 and the second frame 1022 of the connecting element 102 are switched from the open-scissors state to the stacked state. As the keycap 101 is moved downwardly to compress the elastic element 103, the corresponding membrane switch 121 is contacted and pushed by the contacting part 1031 of the elastic element 103. Consequently, the corresponding membrane switch 121 is triggered, and the keyboard device 1 generates a corresponding key signal. When the keycap 101 of the key structure 10 is no longer depressed, the keycap 101 is moved upwardly relative to the base plate 11 in response to an elastic force of the elastic element 103. Meanwhile, the first frame 1021 and the second frame 1022 are switched from the stacked state to the open-scissors state again, and the keycap 101 is returned to its original position.
However, the conventional keyboard device 1 still has some drawbacks. While the keycap 101 of any key structure 10 is depressed and moved downwardly relative to the base plate 11, the keycap 101 collides with the connecting element 102 and the membrane circuit board 12. Under this circumstance, a click sound is generated. When the kinetic energy resulted from collision is transferred downwardly to the metallic base plate 11, the sound is the unpleasant noise to the user. In other words, the conventional keyboard device needs to be further improved.